[Bug c++/21510] Possible bug
--- Additional Comments From sven at clio dot in-berlin dot de 2005-05-17 11:42 --- (In reply to comment #9) Over my dead body. :-) Oh, come on. It isn't that bad an idea to localize substitution failures, isn't it:-) -- Gaby Sven -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
[Bug c++/21510] Possible bug
--- Additional Comments From sven at clio dot in-berlin dot de 2005-05-16 10:22 --- (In reply to comment #7) Is there a way to distinguish between unions (which are not usable as base classes) and classes? If not, the standard is incomplete. You should know that 10 years ago people didn't even imagine the kind of template usages that you are assuming as obvious. Indeed, everyone wants to tell unions from classes now and you bet, it will be possible sometime in the future, likely not using SFINAE at all. I know and accept this. SFINAE is a possible dangerous feature, anyway. It may be better if the ISO standard declares something like the following (incomplete, feel free to propose it to the standard comitee): The pragma statements _Pragme(set, sfinae, on) // enables SFINAE _Pragma(set, sfinae, off) // disables SFINAE _Pragma(reset, sfinae) // sets SFINAE to the previous state control the substitution-failure-is-not-an-error-feature. When setting to on any substitution of a template argument of a class or function declared or defined in the context may fail without an error, if - the statement is syntactical correct - there is a less specific template which could be instantiated without an error. When leaving the context, _Pragma(reset, sfinae) is called automatical. The user is complete responsible for using SFINAE, no further compiler support is standardized. This would localize the feature and alert the user that this is a potential dangerous construct. And it is much more general, possible easier to implement. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
[Bug c++/21510] Possible bug
--- Additional Comments From gdr at integrable-solutions dot net 2005-05-16 19:19 --- Subject: Re: Possible bug sven at clio dot in-berlin dot de [EMAIL PROTECTED] writes: | (In reply to comment #7) | Is there a way to distinguish between unions (which are not usable as base | classes) and classes? If not, the standard is incomplete. | | You should know that 10 years ago people didn't even imagine the kind of | template usages that you are assuming as obvious. Indeed, everyone wants | to tell unions from classes now and you bet, it will be possible sometime | in the future, likely not using SFINAE at all. | | I know and accept this. SFINAE is a possible dangerous feature, anyway. It may | be better if the ISO standard declares something like the following | (incomplete, feel free to propose it to the standard comitee): | | The pragma statements | | _Pragme(set, sfinae, on) // enables SFINAE | _Pragma(set, sfinae, off) // disables SFINAE | _Pragma(reset, sfinae) // sets SFINAE to the previous state Over my dead body. :-) -- Gaby -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
[Bug c++/21510] Possible bug
--- Additional Comments From lerdsuwa at gcc dot gnu dot org 2005-05-15 12:37 --- The code is invalid. In the section 14.8.2 [temp.deduct] paragraph 2 of the standard does not include creating a class with invalid base class. Examples of valid SNINF cases: - Attempting to create an array with an element type that is void, a function type, or a reference type, or attempting to create an array with a size that is zero or negative. - Attempting to use a type that is not a class type in a qualified name. etc. (there are many more they are clearly mentioned in the mentioned part of standard) -- What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution||INVALID http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
[Bug c++/21510] Possible bug
--- Additional Comments From sven at clio dot in-berlin dot de 2005-05-15 14:08 --- (In reply to comment #3) The code is invalid. In the section 14.8.2 [temp.deduct] paragraph 2 of the standard does not include creating a class with invalid base class. If there is no other way to distinguish reliable between unions and classes, add it into the extension list. Unions should be avoided in object oriented design, anyway, but it is a nice-to-have feature. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
[Bug c++/21510] Possible bug
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-15 14:12 --- (In reply to comment #4) If there is no other way to distinguish reliable between unions and classes, add it into the extension list. Unions should be avoided in object oriented design, anyway, but it is a nice-to-have feature. Extensions are bad. Even just bugs in the compiler is a bad thing beause people would think the bug was an extension and start depending on it and then when the bug was fixed, people complain their code no longer compiles. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
[Bug c++/21510] Possible bug
--- Additional Comments From sven at clio dot in-berlin dot de 2005-05-15 14:46 --- (In reply to comment #5) Extensions are bad. Even just bugs in the compiler is a bad thing beause people would think the bug was an extension and start depending on it and then when the bug was fixed, people complain their code no longer compiles. Is there a way to distinguish between unions (which are not usable as base classes) and classes? If not, the standard is incomplete. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
[Bug c++/21510] Possible bug
--- Additional Comments From pcarlini at suse dot de 2005-05-15 15:03 --- Is there a way to distinguish between unions (which are not usable as base classes) and classes? If not, the standard is incomplete. You should know that 10 years ago people didn't even imagine the kind of template usages that you are assuming as obvious. Indeed, everyone wants to tell unions from classes now and you bet, it will be possible sometime in the future, likely not using SFINAE at all. Before posting other messages with this attitude, please, please have a look to the papers available from the ISO Web site: http://www.open-std.org/jtc1/sc22/wg21/ Thanks. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
[Bug c++/21510] Possible bug
--- Additional Comments From sven at clio dot in-berlin dot de 2005-05-12 09:48 --- (In reply to comment #1) I don't think you used SFINF correctly. The substitution of the formal parameter with the actual argument fails, thus it is a form of substitution failure. I do not know, if the example is conforming to the standard. It would be a working method to distinguish between classes and non classes. On the other hand the more stricter interpretation is more safe. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
[Bug c++/21510] Possible bug
--- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-11 11:10 --- I don't think you used SFINF correctly. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21510
